This invention relates to the fabrication of propulsion components and to the resultant structures produced thereby. In a more particular aspect, this invention concerns itself with the fabrication of three-dimensional woven plastic composites for application to rocket nozzles, rocket thrust chambers, integral rocket motors, re-entry heat shields, nose tips, nuclear reactor parts and other structural elements which require a high strength to weight ratio in conjunction with a high temperature capability.
The present interest in high speed and high altitude aircraft, missiles and rockets has created a need for structural elements that are characterized by having the requisite dimensional stability and structural strength to withstand the severe stresses and strains encountered during operation within the high temperature environment of a re-entry regime.
Typically, rocket nozzles, combustion chambers and integral rocket motors are made of composite materials with two-dimensional reinforcing fibers. A number of methods are known for laying the fibers and include a tape wrap and flat wrap in which woven cloth forms are laid perpendicular to the nozzle/motor axis. Another method is the dixie cup wrap in which the cloth forms are canted to the axis. A chopped fabric method, in which the material is randomly put into a mold, compressed and molded into a matrix material is also employed. Conventional filament wound or braided structures have also been used.
However, the structural items made of these materials require a supporting outer steel shell and, in many cases, layers of insulating materials to which they are bonded. This results in an inherent weakness. The bond is always weaker than the fibers and constitutes the basic failure mechanism when heat is applied. "Chunking" describes the failure when chunks of the material come apart at the bond line which is a typical problem of tape wrapped and chopped fabric composites.
Delamination is the typical failure mechanism of cloth braid and filament reinforcements. This results from the fact that the reinforcements are not held together "independent of the bond". The formation of holes cause fraying of the fibers and weakening of the hoop strength in filament wound and braided structures, while the breaking of the edges where chopped fabric is used is still another problem.
The use of a three-dimensional woven fabric has been suggested since blocks of three-dimensional material can be made by pegging, nailing or stitching together many layers of cloth. Bodies of revolution can be machined from these blocks, but this involves serious waste of material and the orientation of the fibers cannot be controlled adequately.
With the present invention, however, it has been found that the aforementioned problems can be overcome by using the polar woven, multidirectional composites of this invention. In fabricating the composites of this invention, longitudinal fibers are arranged, as desired, in up to 360 radial rows around the circumference of a propulsion component, such as a rocket nozzle. Different fibers, such as quartz, carbon, graphite or glass may be arranged from the inside to the outside wall to give the desired characteristics of ablation, insulation or structural integrity. Circumferential fibers are woven into the longitudinals. Different weave patterns may be used, again depending on the desired characteristics.